Support lookup by mapping record index in TPDO and RPDO classes.

These two PdoBase-derived classes only supported numeric access based
on the sequential index, not with the mapping parameter record index
like the PDO class.  Implement a fallback to check that if the regular
index lookup fails.

Author: acolomb

canopen/pdo/base.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import binascii
+import contextlib
 import logging
 import math
 import threading
@@ -169,7 +170,9 @@ def __init__(self, com_offset: int, map_offset: int, pdo_node: PdoBase, cob_base
                 self.maps[map_no + 1] = new_map
 
     def __getitem__(self, key: int) -> PdoMap:
-        return self.maps[key]
+        with contextlib.suppress(KeyError):
+            return self.maps[key]
+        return self.maps[key + 1 - self.map_offset]
 
     def __iter__(self) -> Iterator[int]:
         return iter(self.maps)

test/test_pdo.py

@@ -53,6 +53,7 @@ def test_pdo_getitem(self):
         by_mapping_record = node.pdo[0x1A00]
         self.assertIsInstance(by_mapping_record, canopen.pdo.PdoMap)
         self.assertEqual(by_mapping_record['INTEGER16 value'].raw, -3)
+        self.assertIs(node.tpdo[0x1A00], by_mapping_record)
         by_object_name = node.pdo['INTEGER16 value']
         self.assertIsInstance(by_object_name, canopen.pdo.PdoVariable)
         self.assertIs(by_object_name.od, node.object_dictionary['INTEGER16 value'])